OPERABILITY Basis

OPERABILITY of the AC electrical power sources ensures sufficient power is available for: (1) safe shutdown of the facility, and (2) mitigation and control of accident conditions. The minimum independent and redundant AC and DC power sources satisfy the requirements of GDC 17 of 10 CFR Part 50, Appendix A.

The sources are consistent with initial condition assumptions in the accident analyses — at least two independent sets of onsite AC and DC sources must be OPERABLE during an accident with an assumed loss of all offsite power and a single failure of one onsite AC source.

Action Statement Logic

ACTION requirements specify different completion times commensurate with the level of degradation:

• Action a.2 (one train without offsite power): assurance that a coincident single failure of the associated DG will not cause a complete loss of all critical redundant required systems.
• Action b.2 (one DG inoperable): assurance that a loss of offsite power will not cause a complete loss of safety function of critical systems.
• Action d.2 (two offsite circuits inoperable): assurance that an event plus a coincident single failure will not cause complete loss of redundant required safety functions.

These systems are powered from an independent AC electrical power train. Redundant required systems are not necessarily powered from AC electrical sources (e.g., the turbine-driven AFW pump is redundant to the motor-driven pumps).

When a system or component is determined inoperable solely because its normal power source OR its emergency power source is inoperable, it may still be considered OPERABLE provided the applicable cross-train action (a.2, b.2, or d.2) is satisfied.

LCO 3.0.4.b is NOT applicable to an inoperable DG — a risk assessment cannot be used to enter a MODE or other specified condition in the Applicability with an inoperable DG.

Completion Time Rationale

The completion time allows the operator time to evaluate and repair. An exception to the normal “time zero” for the allowed outage clock exists: the clock starts only upon discovery that BOTH (a) one train has no offsite power, the DG is inoperable, or two offsite circuits are inoperable, AND (b) a required system on the other train is inoperable.

The remaining OPERABLE AC supplies are adequate on a component basis — single failure protection may have been lost, but the safety function itself has not been lost.

The completion time for Condition d (loss of both offsite circuits) is reduced to 12 hours, shorter than the time allowed for one train without offsite power (Action a.2). Reg Guide 1.93 allows 24 hours for two required offsite circuits inoperable, but that assumes two complete safety trains OPERABLE. The shorter 12-hour time applies because a concurrent redundant required system failure cannot be ruled out.

14-Day EDG Allowed Outage Time Extension

LCO 3.8.1.1, Action b.4.a.2 allows the EDG AOT to be extended from 72 hours to 14 days with the following commitments (when utilizing extended EDG AOT > 72 hours and < 14 days):

1. When a DG is removed from service, the TDAFW pump and its supporting systems must be OPERABLE
2. Voluntary entry is not permitted during adverse weather conditions
3. The system load dispatcher is contacted once per day regarding grid perturbations
4. Licensed operators are trained on the SPS (supplemental power supply) purpose and use
5. Operating crews are briefed on the EDG work plan and LOOP/SBO procedures
6. If any commitment is not met, enter the corrective action program

DG surveillance is per Reg Guide 1.9 (DG set capacity for standby power), Reg Guide 1.108 (periodic testing of DGs), and Reg Guide 1.137 (fuel oil testing). Surveillance frequency is based on operating experience, reliability, and plant risk, controlled under the Surveillance Frequency Control Program.

Voltage and Frequency

The minimum voltage and frequency values in the SR ensure the EDG can accept DBA loading while maintaining acceptable voltage and frequency. Stable operation at normal voltage and frequency is also essential for OPERABILITY — no time constraint is imposed on voltage/frequency oscillations to dampen.

The narrower band for steady-state frequency ensures the EDG is not in an overloaded (isochronous steady state) condition during accident conditions. Steady state is achieved after 1 minute with all loads sequenced. The narrower band for steady-state voltage ensures the voltage regulator protects against over-voltages during an accident. A wider voltage band is appropriate when the EDG is paralleled to the grid (governor droop mode).

All voltages and frequencies in SR 4.8.1.1.2 are representative values — instrument inaccuracies for EDG voltage and frequency are administratively controlled.

Start Time and Standby Condition

The 13-second start time requirement is based on the Westinghouse assumption of 15 seconds from occurrence to electrical power to the first sequenced safeguards pump (BURL-3011 dated Nov 13, 1974; BURL-1531 dated July 27, 1970). Supporting times are in UFSAR Section 15.4.

“Standby condition” means the engine state immediately prior to starting for the surveillance. Lube oil temperature must be between 100 °F and 170 °F; the minimum lube oil temperature for an OPERABLE diesel is 100 °F.

The minimum specified AC and DC sources during shutdown and refueling ensure: (1) the facility can be maintained in a shutdown or refueling condition for extended periods, and (2) sufficient instrumentation and control capability is available for monitoring.

Specs 3.8.2.2, 3.8.2.4, and 3.8.2.6 include movement of irradiated fuel assemblies — these requirements ensure adequate electrical power for Fuel Handling Building ventilation.

An offsite circuit is considered inoperable if it is not available to all required trains — the option exists to declare all required features associated with that circuit inoperable instead.

With both required DGs inoperable, the minimum required diversity of AC power is not available — suspend CORE ALTERATIONS, irradiated fuel movement, and positive reactivity additions.

The 125V DC batteries provide control power for switchgear operation, diesel generator starting, reactor trip breaker control, and emergency instrumentation. OPERABILITY of the DC sources ensures sufficient power for safe shutdown and accident mitigation, consistent with GDC 17. The 2-hour completion time for a battery reflects the critical importance of DC power for safety functions.

The three 28V battery supplies power the reactor trip breaker undervoltage (UV) coils — loss of these supplies causes a reactor trip (fail-safe design). The 48-hour completion time for one inoperable 28V supply reflects that the remaining two supplies maintain trip capability.

The minimum specified DC source during shutdown and refueling ensures sufficient instrumentation and control capability for monitoring and maintaining the facility in a safe shutdown condition for extended periods. Requirements in Specs 3.8.2.2, 3.8.2.4, and 3.8.2.6 that address movement of irradiated fuel assemblies ensure adequate electrical power for Fuel Handling Building ventilation.

Containment electrical penetrations and penetration conductors are protected by either deenergizing circuits not required during reactor operation, or by demonstrating OPERABILITY of primary and backup overcurrent protection circuit breakers during periodic surveillance.

Surveillance frequency is based on operating experience, equipment reliability, and plant risk, controlled under the Surveillance Frequency Control Program.